The present invention relates to an optical space communication apparatus such as an optical space communication transceiver for sending an optical signal in a free space to perform optical communication.
In a conventional optical space communication apparatus shown in FIG. 1, a transmitter 37 comprises a means (modulating circuit) 31 for modulating an input electrical signal into a signal having a format suitable for optical space communication, a means (optical element) 32 for amplifying the modulated signal, driving a light-emitting element such as a light-emitting diode or a semiconductor laser on the basis of the amplified signal, and converting the electrical signal into an optical signal, and a means (optical system) 33 for causing an optical member such as a lens to convert a beam emitted from the light-emitting element into a fan beam having a necessary spread angle. A receiver 38 comprises a means (optical system) 34 for causing an optical member such as lens to focus a beam from the transmitter 37 onto a photodetecting element such as a photodiode, a means (optical element) 35 for causing the photodetecting element to convert the optical signal into an electrical signal and amplifying the electrical signal to a signal having a predetermined level, and a means (demodulating circuit) 36 for demodulating into a signal of the original format the electrical signal converted from the optical signal.
In this apparatus, strict positional alignment is required between the optical systems 33 and 34 such as lenses and the optical elements 32 and 35 such as a light-emitting element and a photodetecting element. The modulating and demodulating circuits 31 and 36 must be mounted near the optical elements in consideration of the mounting forms since these circuits 31 and 36 process high-frequency signals.
Since this apparatus is used outdoors for a long period of time, it requires a rigid, waterproof housing. The functional components such as the transmitter and the receiver must be appropriately arranged inside the housing.
In addition, direction and angle adjusting means are required to appropriately direct the transmitter consisting of the functional components protected in the housing toward the receiver consisting of its functional components. These adjusting means are generally mounted in the lower portion of the housing. Greater precision is required in angular adjustment when a communication distance is increased.
In the conventional structure, however, the housing is disassembled at the time of internal failures and repairing. When failed components are the optical elements or after repairing, those portions 32 and 35 near the optical elements, the optical elements or their neighboring portions 32 and 35 must be aligned with the optical systems 33 and 34 such as lenses. It is difficult to perform this adjustment on the spot. The associated components must be removed and adjusted in an appropriate location, such as a factory. When the repaired components are remounted in the housing, the angle of the apparatus as a whole must also be adjusted.
Even if a failed component is different from those described above, it is difficult to check the failed component after the waterproof, rigid, outdoor housing is disassembled. During disassembly, the position of the optical element with respect to the optical system may be shifted or the angle of the apparatus as a whole may deviate from the correct angle. Therefore, in such a case, readjustment is required. Similar problems are posed at the time of inspection or the like except for the absence of internal failure.
As described above, although the apparatus is used outdoors for a long period of time, it must be capable of achieving highly accurate positional and angular adjustment. Thus, it is difficult to appropriately install, repair, and maintain the apparatus. Therefore, conventional optical space communication apparatus are not easily handled by a user.
Furthermore, an optical space communication apparatus may be used over a range from a short distance of 10 m to a long distance of several km. As the communication distance is increased, greater accuracy in angular precision, optical characteristics, and electrical characteristics (e.g., reception sensitivity) are required. Transmission signals have different forms, i.e., analog and digital signal forms, and the communication speed ranges from a low speed which can be easily controlled to a high speed. When transmission signal speed is increased, higher performance is required in electrical circuits, light-emitting and light-receiving elements, and modulating and demodulating circuits of the transmitter and the receiver. In order to satisfy these various needs, products may be developed in a range from a low-end product to a high end product depending on the purposes of applications. Alternatively, or the specifications of the apparatus may be designed to comply with the most strict requirements. However, such an implementation results in high cost, without any economical advantage.
It is, therefore, an object of the present invention to provide an optical space communication apparatus which can solve all problems posed by installation, repairing and maintenance of the apparatus, and meet various requirements.
In order to achieve the above object of the present invention, an optical space communication apparatus (transmitter and receiver) according to the present invention comprises a plurality of modules which can be separated from each other. Positions of optical elements such as an optical system, or a single optical element, as well as a CCD of the modules are adjusted beforehand to have a predetermined relationship with coupling reference portions of the modules which constitute a common reference at the time of coupling, thereby allowing automatic positioning at the time of coupling of the modules. Alternatively, one of the plurality of modules may have a stand reference portion having a predetermined positional relationship with its optical element and its coupling reference portion. The stand reference portion is coupled to the reference portion of the stand whose angle can be adjusted, thereby constituting the common reference.